The invention relates to an automated transmission of a reduction gearing design having a plurality of discrete transmission stages and power branches for a motor vehicle and to a method of operating such a transmission.
U.S. Pat. No. 5,381,703 and DE 100 51 354 A1 disclose transmissions of a reduction gearing design, in which, in direct gear, an input shaft of the transmission is connected to an output shaft of the transmission so as to rotate with it and without intermediate intermeshing gearwheels. In such a direct gear the countershaft is decoupled from the input shaft and the output shaft gear shifting elements are shifted into a neutral position. In this way it is possible to improve the efficiency in direct gear since the countershaft and transmission elements, which are possibly connected to the countershaft, are not rotating. As a result, it is possible, on the one hand, to reduce the inertia of the drive train. On the other hand, bearing friction and any churning losses of the countershaft with assigned transmission elements in an oil sump do not rotate so that the power loss is minimized.
Furthermore, DE 198 53 824 A1 discloses a double clutch transmission in which the drive torque in one component transmission is transmitted via a countershaft while in another component transmission a direct gear is provided.
If the latter component transmission is activated via the double clutch in direct gear, this is accompanied by a release of the drive connection to the countershaft of the first component transmission by releasing the assigned clutch of the double clutch so that the countershaft is also decoupled from an input shaft of the transmission.
Furthermore, documents DE 27 36 834 A1 and DE 27 36 929 A1 disclose a vehicle transmission of a reduction gearing design, in which power branching takes place in all the forward gears as well as the reverse gear with the exception of a direct, highest gear. For the power branching, a gearwheel of a countershaft has a drive connection both to the one countershaft and to the other countershaft via an intermediate gearwheel which is mounted so as to be rotatable with respect to a main shaft. Power is output by combining the two power paths at a gearwheel which is mounted so as to be rotatable with respect to the main shaft and which has a drive connection at its circumference to, in each case, one gearwheel which has a fixed drive connection to a countershaft. Accordingly, the power is divided between the two countershafts so that it is ensured that the mechanical loading for transmission elements lying in the power flux downstream of the branching point is also halved. However, the abovementioned power branches can be combined only if the two countershafts rotate at the same rotational speed, which makes the periphery conditions for dividing the power outputs between the power branches and the configuration of the possible transmission ratios more difficult.
Finally, WO 03/025431 A1 discloses an automated transmission for a motor vehicle which has a plurality of discrete transmission stages and is of a reduction gearing design. The countershaft has a continuous drive connection to a transmission input shaft via an input constant. At the output end, a three-shaft transmission or variable-ratio gear unit is connected downstream of the reduction gearing unit and thus forms a further component transmission. At the lowest gears, a transmission element of the three-shaft transmission is locked by means of a brake, while the reduction gearing unit is embodied in a customary fashion with a single power branch which extends via the countershaft. For further transmission gears power branching takes place, with a sun wheel of the three-shaft transmission being connected directly to the transmission input shaft in a first power branch, while the second power branch extends via the countershaft. The two power branches are joined in the three-shaft transmission, with the transmission output shaft being coupled to the web of the three-shaft transmission.
Continuously variable transmissions relate to a different branch of technology in which it is necessary to ensure the continuously variable ratio change in transmission power branch by what is referred to as a CVT, together with combination of the power branches in a planetary gear unit. Such transmissions, for example corresponding to DE 199 44 792 A1, DE 196 31 216 A1, U.S. Pat. No. 4,682,511, U.S. Pat. No. 4,662,240 are therefore not transmissions of the generic type with a plurality of discrete transmission stages.
It is the object of the present invention to improve a transmission of the generic type with different shift states, a number of gears that can be implemented and also the synchronization procedures.
Furthermore, it is an object of the invention to improve a method of operating a transmission in a motor vehicle by reducing losses, wear, noise, shifting times and/or shifting processes.